Percussive circuit and assembly



Dec. 22, 1959 w, u cH, JR 2,918,576

PERCUSSIVE CIRCUIT AND ASSEMBLY Filed Nov. '15, 1956 INPUT -"1- 1 ,1 2 i ,0 9: 14 r r i 1, t. .1. m .1. &7 ;1 15 2 12 121T J flab T 726T 1 111 A/A/TL 116/1 IN V EN TOR, %A 7-5 MAM/4 ATTORNEYS.

United States Patent f PERCUSSIVE CIRCUIT AND ASSEMBLY Walter Munch, Jr., Covington, Ky., assignor to The Baldwin Piano Company, Cincinnati, Ohio, a corporation of Ohio Application November 13, 1956, Serial No. 621,807

11 Claims. (Cl. 25027) In a copending application of Alfred J. Bissonette and Frank I. Kramer, Jr., Serial No. 621,769 filed November 13, 1956, and entitled Electronic Musical Instrument, assigned to the same assignee, there is described an electronic musical instrument having provision for percussive effects. In this instrument the percussive effects a e obtained by providing, for oscillations derived from the normal oscillation generators of the instrument, gating or percussive circuits each normally biased to cut-off. Upon the closing of a switch, the tube in such a stage is rendered transmissive to the oscillations, which are passed selectively through vacum tube tone control means and to an output system comprising an amplifier and a loud speaker. The gating or percussive circuit contains a resistor and capacitor network, hereinafter referred to as a time-constant circuit. Upon the opening of the switch aforesaid, .the cut-off bias on the tube is not instantaneously restored, but only after the delaying action of the time-constant circuit, as in the charging or discharging of the capacitor. This action results in a gradual decay of the transmitted oscillations in accordance with a predetermined pattern, such as an exponential curve. Thus, if the note is played staccato, i.e. if the switch be closed and substantially immediately opened again, the tone decay characteristic becomes audibly significant, and the reproduced tone has the percussive characteristics of tones derived from bells, bars or plucked or struck strings. For the general arrangement of such an instrument and assembly of apparatus, reference is made to the said copending application.

A primary object of the present invention is the provision, first, of an improved gating or percussive circuit and, second, of an improved assembly or combina- .tion of percussive circuits.

It is an object of the invention to provide a gating circuit combination having fewer components.

It is an object of the inventionto provide means associated with a current-valve device of the type in which the audio-frequency gain isresponsive to a DC. bias, whereby said gain may be made to decrease from one valueto another at selectablev rates without affecting the value of the maximum gain;

It is an object of the invention to provide a percussive circuit having improved means for controlling the extent of the decay, and in particular to provide a circuit in which the extent is controlled by changing the potential to which the time-constant capacitor charges or discharges. i

It is an object of the invention to provide a circuit which is not only effective in eliminating key clicks and disturbances of amplitude when several notes are played together or in rapid succession, but is also effective in one species in the prevention of ciphers if any of the timeconstant capacitors becomes leaky.

These and otherobjects of the invention, which will be set forth hereinafter or-will be apparent toone skilled in the art upon reading these specifications, are accomplished'by that arrangement of parts and in those circuits 5 2,918,576 Patented Dec. 22, 1959 of which certain exemplary embodiments will now be described. Reference is made to the accompanying drawings wherein:

Fig. l is a circuit diagram (simplified) of a single gating or percussive stage.

Fig. 2 is a circuit diagram of a modified form of percussive stage.

Fig. 3 is a circuit diagram showing a plurality of gating stages in association.

Referring first to Fig. 1, there is shown a gating stage comprising a thermionic triode 1 having a plate 2, a grid 3, and a cathode 4. The plate of the tube is connect-d to a source of positive voltage marked B+ through a resistor 5. The grid of the tube is connected to a source of oscillations (not shown) through a capacitor 6. The source of oscillations will be an oscillator, preferably an electronic oscillator producing oscillations which are rich in harmonics. A source of cathode-biasing voltage is connected to the cathode 4 as shown, and between the points marked +V and V in the diagram. A voltage divider, comprising series resistances 7, 8 and 9, is also connected between +V and V. There is a connection between the grid and the cathode containing a resistor 10 and a normally open switch 11. A timeconstant capacitor 12 is connected to the grid-cathode lead on the grid side of the switch 11. The capacitor 12 is returned to the cathode 4 as shown. A resistor 15 is connected to the grid-cathode circuit on the grid side of the switch; and this resistor has connection with the switch arm of a multi-contact switch 16. The contacts of this switch are connected to the aforesaid resistive divider as shown, so that upon selectively operating the switch, the grid circuit will return to desired points on the voltage divider comprising resistors 7, 8 and 9.

There is an output circuit, usually containing a capacitor 17 and a resistor 18 connected to the plate of the tube. Through this output circuit oscillations may be derived when the tube is in a condition to transmit them. The oscillations so derived, with appropriate tonecolor modification, may be sent to an output system (not shown) for conversion into audible sound. It will be understood that the switch 11 will be operated by a playing key of the musical instrument, to be closed when the key is struck and opened when the key is released.

The operation of the percussive circuit of Fig. 1 is as follows:

When the switch 11 is open, as shown, the time delay capacitor is in charged condition, the value of the charge being determined by the position of the selector switch 16, but the bias on the tube being in any event sufiicient to'prevent transmission of oscillations by the tube 1 Upon closing of the switch 11, the capacitor 12 is discharged through the switch, and the grid 3 is brought to the same potential as the cathode 4. Under these conditions, the input oscillations are passed by the tube 1 to the output circuit. The amplitude of the oscillations passed by the tube remains the same (while the switch 11 is closed) irrespective of the position of the switch 16.

When the switch 11 is again opened, the capacitor 12 charges up to a level determined by the position of the switch 16, and the oscillations transmitted by the tube decay to-an inaudible level over a time interval determined by the time required to charge the capacitor 12 to the cut-off voltage of the tube 1. Since, however, the time required to charge the capacitor to the cut-off voltage dependsupon the potential applied to the series combination ofresistor 15 and capacitor 12, it will now be clear that the switch 16 and resistive network 7, 8 and 9 furnish an effective way of selecting and varying the time characteristics of the decay, without affecting the level of amplification of the tube 1 when switch 12 is closed.

In Fig. 2- like parts have been given like index nu 3 merals. In the circuit of this figure, the capacitor 12 is returned to the cathode 4 through a much larger capacitor 14, and is also returned to V through a resistor 13. Thus, certain additional advantages are gained as will hereinafter be set forth.

The voltage divider may be grounded or connected to a common return for all circuits either at 19 or at 20. When the switch 11 is open, the tube 1 will be biased to cut-off in either event. When the ground connection is at 19, the cathode will be biased positively with respect to the grid which will have zero bias. When the ground connection is at 20, the grid will be biased negatively with respect to the cathode which will be at ground potential.

The operation of the percussive circuit of Fig. 2 is as follows:

If the switch 11 is closed, the capacitor 12 will become charged through resistor 13 to a value determined by the potential difference between +V and V. There is a slight time delay while this occurs, but this is normally nugatory so far as producing any audible effect is concerned. When the capacitor 12 has charged to the aforesaid value, there will be a zero potential difference between the grid 3 and the cathode 4, so that the tube is rendered conductive, and will transmit to the output circuit in the usual manner electrical oscillations applied to the grid through the capacitor 6. The transmission will, of course, continue for so long as the switch 11 remains closed.

When, however, the switch 11 is opened, the capacitor 12 will begin to discharge through the resistor 15 to the potential of the point on the voltage divider determined by the setting of the switch 16, the potential of all such points being sufficient to bias the tube to cut-off. The rate of discharge will depend partly upon the value of resistor 15 and partly upon the potential of the point on the voltage divider to which the switch 16 is connected. The switch 16 thus selects the rate of the decay without affecting the over-all gain of the tube when switch 11 is closed.

In circuits of the type of Fig. 1, where the time-constant capacitor is returned directly to the cathode, a cipher may be p oduced in the instrument if the capacitor becomes leaky. i.e. the leaky capacitor may destroy the cutoff bias on the tube and cause the note to sound irrespective of the operation of the switch. In the species of this invention illustrated in Fig. 2, the possibility of ciphers is eliminated by returning the capacitor 12 to a source of potential highly negative with respect to the cathode. This gives rise to another problem in the operation of an instrument having a plurality of percussive ir uits. If a number of notes are played simultaneously or in rapid succession, the large charging current drawn by the time-constant capacitors may produce key clicks because of surge currents through the voltage divider. In the circuit of Fig. 2, key clicks are eliminated by returning the time-constant 12 through the resistor 13 and storage capacitor 14. The capacitor 14 is charged from the voltage divider, and the time-constant capacitor can thus become charged (when the switch 11 is closed) from the charge available on the much larger storage cana itor, thus minimizing surge currents in the voltage divider.

In Fig. 3 there is shown a gang combination of four percussive circuits, such as may be employed in the system of the Bissonette and Kramer application noted above. Like parts have been given like index numerals. Each pe cussive circuit has its own thermionic element exemplified by the tubes 1, la, etc. although it will be evident that instead of separate tubes. separate halves of double triodes may be used. Each percussive circuit has its own grid resistor 10, 10a, etc., and its own time-constant circuit comprising the capacitor 12. 120. etc., and the resistor 15, 1511, etc. However, the capacitors of the four time-constant circuits are returned to the cathodes through a common storage capacitor 14, and to the voltage divider through a common resistor 13. The cathodes of the tubes are connected together and to the source of cathode-biasing voltage indicated at +V. Each percussive circuit has a separate switch 11, 11a, etc. with a common return to the cathode lead. There is a common voltage divider comprising resistors 7, 8, 9 and selector switch 16, forming a means for selecting the rate of decay. Each percussive circuit has its own input circuit, containing its own coupling capacitor 6, 6a, etc., and connected respectively to sources of oscillations in the generating system (not shown) of the instrument.

In former gang circuit arrangements, the output signals from the several percussive circuits were derived across separate plate resistors and combined by means of four summing resistors before going to the filters. In the arrangement of the present invention, the plates of the several tubes are connected together, and there is a common plate resistor 5. There is also an output circuit common to the four, ganged percussive circuits and containing a common capacitor 17 and resistor 18.

Thus, the circuit arrangements of this invention have the important advantage of using fewer components. The arrangement of Fig. 3 tends to produce somewhat more intermodulation distortion; but not only is this distortion minimized by using a low value for the plate resistor 5, but it has been found that the filter which follows in the Bissonette and Kramer system is effective in reducing the remaining distortion to an acceptable level. It will be obvious that two or more of the circuits of Fig. 1 may be commonly fed from a plate supply as shown in Fig. 3.

Modifications may be made in the invention without departing from the spirit of it. The principles of the invention may be practiced with current-valve devices other than thermionic tubes as, for example, transistors. The invention having been described in certain exemplary embodiments. what is claimed as new and desired to be secured by Letters Patent is:

1. n a musical instrument of the tvpe wherein a source of electrical oscillations corresponding to a musical tone is connectable to an output system for translation of the oscillations to sound, a percussive circuit comprising a current-valve device having an input circuit connectable to such source and having an output circuit connectable to said output system, the amplitude of the oscillations transmitted to said output system by said current-valve being responsive to a direct current bias applied to said device, a time-constant circuit having a resistor and a capacitor coupled to said device. voltage-divider means coupled to said device for supplying a direct current bias operative to control transmission of oscillations by said current-valve to said output system, key-switch means closable for momentarily changing the charge on said capacitor to produce transmission in said current valve device, and selector means connected between said voltage-divider means and said resistor and capacitor for providing a variable direct current level which said capacitor may assume when said key switch means is actuated, whereby the time of decay of oscillations in said output circuit may be changed.

2. In a musical instrument of the type wherein a source of electrical oscillations corresponding to a musical tone is connectable to an output system for translation of the oscillations to sound, a percussive circuit comprising a current-valve device having an input circuit connectable to such source and having an output circuit connectable to said output system, the amplitude of the oscillations transmitted to said output system by said current valve being responsive to a direct current bias applied to said innut circuit. a time-constant circuit having a resistor and capacitor coupled to said input circuit, voltage-divider means coupled to said input circuit for supplying a direct current bias to said input circuit operative to block transmission of oscillations by said currentvalve to said output system, key-switch means closable for momentarily discharging said capacitor to unblock said current-valve device, and selector means connected between said voltage-divider means and said resistor and capacitor for providing a variable direct current level to which said capacitor may charge when said key-switch means is opened, whereby the time of decay of oscillations in said output circuit may be changed.

3. In a musical instrument of the type wherein a source of electrical oscillations corresponding to a musical tone is connectable to an output system for translation of the oscillations to sound, a percussive circuit comprising a current-valve device having an input circuit connectable to such source and having an output circuit connectable to said output system, the amplitude of the oscillations transmitted to said output system by said current-valve being responsive to a direct current bias applied to said device, a time-constant circuit having a resistor and a capacitor coupled to said device, voltagedivider means coupled to said device for supplying a fixed direct current bias operative to control transmission of oscillations by said current-valve to said output system, key-switch means closable for momentarily changing the charge on said capacitor to produce transmission in said current-valve device, and selector means connected between said voltage-divider means and said resistor and capacitor for providing a variable direct current level which said capacitor may assume when said key-switch means is opened whereby the time of decay of oscillations in said output circuit may be changed.

4. In a musical instrument of the type wherein a source of electrical oscillations corresponding to a musical tone is connectable to an output system for translation of the oscillations to sound, a percussive circuit comprising a current-valve device having an input circuit connectable to such source and having an output circuit connectable to said output system, the amplitude of the oscillations transmitted to said output system by said current-valve being responsive to a direct current bias applied to said input circuit, a time-constant circuit having a resistor and a capacitor coupled to said input circuit, voltage-divider means coupled to said input circuit for supplying a fixed direct current bias to said input circuit operative to block transmission of oscillations by said current-valve to said output system, key-switch means closable for momentarily charging said capacitor to unblock said current-valve device, and selector means connected between said voltage-divider means and said resistor and capacitor for providing a variable direct current level to which said capacitor may discharge when said key-switch means is opened whereby the time of decay of oscillations in said output circuit may be changed.

5. The combination claimed in claim 4, including a storage capacitor in series with said time-constant capacitor and said key-switch, said storage capacitor being normally charged from said voltage-divider, whereby when said key-switch is closed, said time-constant capacitor is charged from the charge on said storage capacitor.

6. In a percussive circuit, thermionic means compris ing a plate, a grid, and a cathode, an input circuit to the cut-oh bias is restored upon discharge of said capacitor,

said means for applying said cut-off bias comprising a voltage-divider, and an adjustable connection between the time-constant circuit and said voltage-divider effective to determine the potential to which said capacitor discharges.

7. The structure claimed in claim 6 wherein said capacitor is grounded through a resistor and returned to said cathode through a storage capacitor of large size.

8. In a percussive circuit, a thermionic triode comprising a plate, a grid, and a cathode, an input circuit to said grid comprising a capacitor, means connecting said cathode to a source of positive potential suflicient to bias said triode combination to cut-01f, means including a resistor for connecting said plate to a source of positive potential, an output circuit containing a capacitor and a resistor connected to the plate side of said last mentioned means, a grid resistor connected to said grid, a time-constant circuit comprising a first resistor and a capacitor connected in parallel to said grid resistor, said capacitor having a connection with ground through a second resistor, a voltage-divider connecting said cathode and ground, a variable connection between said first resistor and said voltage-divider, and a connection including a switch between the grid side of said time-constant circuit and said cathode.

9. The structure claimed in claim 7 including a connection between said time-constant capacitor and said cathode including a relatively larger storage capacitor.

10. A gang combination of a plurality of the percussive circuits of claim 8 in which each thermionic combination has its own input circuit, its own grid resistor, its own switch, and its own time-constant circuit, but in which a common voltage-divider is variably connected to said first resistors of the several circuits.

11. A gang combination of the percussive circuits of claim 9 in which each thermionic combination has its own input circuit, its own grid resistor, its own switch, and its own time-constant circuit, but in which a common voltage-divider is variably connected to the said first resistors of the several circuits, and in which the timeconstant capacitors of said several circuits are connected together and are returned to the cathodes of said thermionic combinations through a single, large capacitor.

References Cited in the file of this patent UNITED STATES PATENTS 2,173,888 Smiley Sept. 26, 1939 2,354,699 Owens Aug. 1, 1944 2,577,753 Hanert Dec. 11, 1951 2,639,639 Schmidt May 26, 1953 

